1. Field of the Invention
The present invention generally relates to a technique for interaction between a scheduler and a power controller in a wireless communication system. More particularly, the present invention relates to a technique for joint scheduling and power control among a Base Station (BS) and Relay Stations (RSs) in order to increase fairness and transmission efficiency on a downlink in a Distributed Antenna System (DAS) using frequency reuse and common power control.
2. Description of the Related Art
In a conventional cellular system, a scheduler typically selects packets to be transmitted to Mobile Stations (MSs) according to their priority levels. Therefore, every MS and every BS have a common scheduler. MSs are known to suffer from different signal attenuation and interference according to their locations at given point in time. This difference in signal attenuation and interference results in the problem that when MSs are allocated the same transmit power, they have different Signal-to-interference and Noise Ratios (SINRs). In an attempt to make the SINRs of the MSs uniform, a power controller allocates higher power to remote MSs relative to the BS (or RS) and lower power to nearby MSs relative to the BS (or RS).
In a DAS that operates using frequency reuse and common power control, the link between a BS and an RS is established by a dedicated line, such as an optical fiber, and each RS functions like the BS, in that each RS serves as an antenna of the BS. The BS and the RS have their independent service areas and frequencies that can be reused in the service areas. It may occur that two MSs are located near to the boundary between the service areas, although in the different service areas and sharing the same channel. When a scheduler selects packets for the MSs, the MSs have low SINRs due to interference from the neighboring service areas, and thus there is a high probability that transmission of the packets to the MSs will result in failure. If a high power level is allocated to one or both of the MSs to increase their SINRs, a resultant increase in mutual interference nullifies the effect of the power control increasing the power level. The reason for the increase in mutual interference that nullifies the effect of the increased power level is because the power control is being performed after the scheduling. As scheduling and power control take place independently, data transmission to the MSs is failed and/or a minimum data rate is not met, thereby causing an outage. Accordingly, as the number of MSs increase and the use of the networks increase, the likelihood of the aforementioned problems will likely increase as well. Thus, there is a need in the art to provide a solution to this problem.